Official Luthiers Forum!

I have my PID-controlled heating blanket completed, and I'm able to hold it at exactly 325 degrees F (or any other temp) nicely. I got two pieces of .010" spring steel, and I degreased them with Naptha. When I layer the blanket between the two pieces of spring steel and lay the entire assembly on the bending form however, the steel produces lots of smoke.

When everything is cooled off and I can pick up a steel slat I notice that wherever it made contact with the blanket there's a greasy film on it that feels like silicone (dry and slick, feels different than oil). If I clean off the film with Naptha and start with a squeaky clean slat it gets greasy again when heat is applied.

I bought an Omega silicone heating blanket - The blanket alone doesn't smoke, just the slats where they make contact with it. I guess I could always place the wood above the slat (the topside stays clean), but the smoke is unpleasant and I need to keep a fan blowing out the window the entire time it's running. 

 

Are you sure it is the slats and not wood dust on the blanket? I use spring still slats and the only time I get smoke is either if I scorch a set or the blanket has some accumulated wood dust on it.

[QUOTE=Hesh1956]My blanket smoked for a while and I thought that it was the slats since the blanket did not smoke on it's own. But the slats, by concentrating the heat of the blanket, acted to let the blanket get just over the threshold to where it would smoke.

I suspect that it will improve with use and a few dry runs.

AND!!!! Welcome to the OLF Mike!!!!!    We are very glad to have you here![/QUOTE]

Thanks! I've been lurking for a while and I'm finding it to be a great and inspirational site!

What you mentioned about the blanket makes sense. I'm a bit perplexed about the greasy residue on the steel though.

The grease or oil on the spring steel I don't get. If you are not wrapping your wood in foil of kraft paper you are going to get resin on your slats from the heated wood, but nothing should be coming off the blanket. Unless the blanket was coated with something for shipping, which I see no reason for. But I get my blankets From John at Blues Creek. If it is silicone on the blanket or slats for what ever reason, the smoke is the lest of your issues as silicone will make your wood pretty much unfinishable.

We use stainless spring steel slats...three of them. The wood is between layer one and two, and the blanket is between two and three. We wrap the wood in paper as well.   This way we have no direct contact between the heating blanket and the wood which makes the heat more even on the wood. The ss spring coil stock is available from McMaster Carr.   We're using Doolin-style benders that allow for positive indexing of the butt end of the side slats, and these benders are much easier to use than the Fox benders we used to use. We're about to try two blankets to get faster drying of the sides on the inside.

    Some spring steel is lacquered. If it's stainless steel it isn't going to rust in the box, spring steel definitely will. Should burn off, could be a reaction to something in the silicone!

_________________
Billy Dean Thomas
Covina, CA

"Multi famam, conscientiam, pauci verentur."
(Many fear their reputation, few their conscience)

     The blueing process on the steel may be part of the issue. It you didn't get all the oils off that are part of the process from the manufacturer that may be part of the problem,
     You need to use
1 mineral spirits to remove the oils and greases
alcholol and naphtha to pull off silicones and waxes
then you should be fine
john hall
also NEVER PUT BLUED STEEL NEXT TO WOOD this will cause you some very bad problems
john hall

Where can I find .010"-.012 spring steel slats? I've check about a coulpe dozen shops in my area and could'nt find them. Thanks

[QUOTE=tippie53]     The blueing process on the steel may be part of the issue. It you didn't get all the oils off that are part of the process from the manufacturer that may be part of the problem,
     You need to use
1 mineral spirits to remove the oils and greases
alcholol and naphtha to pull off silicones and waxes
then you should be fine
john hall
also NEVER PUT BLUED STEEL NEXT TO WOOD this will cause you some very bad problems
john hall[/QUOTE]

Thanks for the tip - I'll give that a try and see if it helps. I wiped each slat down with naptha and thought that would have degreased them by itself.

[QUOTE=Mackie]Where can I find .010"-.012 spring steel slats? I've check about a coulpe dozen shops in my area and could'nt find them. Thanks [/QUOTE]

Mcmaster-Carr, search for "spring steel shim stock". I bought 6"x50"x.010 rolled spring steel stock which I cut to 36" lengths. After receiving them, I wrapped a roll in a folded up towel so the end of the roll was exposed, slid the cardboard ring to the end of the roll and cut the ring through with a knife, with my foot on the roll. The towel held the roll safely as it popped open a little (like a Pillsbury dough container), then I kicked it away from me and let it unfurl at a safe distance . I'd hate to think what would happen if someone was to pop off the cardboard ring from a tightly constricted roll of spring steel as it exploded open with those razor sharp edges!

   I stock .015   I find this the perfect thickness. The little extra support the wood well and creat some thermal mass
john hall

I got .010" Stainless through Fastenal. Don't know if you have one in your area.

_________________
Horton, MI

mcmaster carr

Thanks everyone, for the spring steel dealers. Mike, I hope you find the source of your problem.

If you live in an area that has a lot of equipment manufacturing most of the steel vendors tht support the local manufacturing will carry it in 6" widths and cut to desired length.

Thanks Todd and MichaelIP. I think I'll give John Hall a call.